1) Field of the Invention
The present invention is directed to directional antennas and antenna radomes.
2) Description of Prior Art
The range of an antenna is based on its power divided by its beam width, among other variables. Therefore, directional antennas operate at greater ranges than omni antennas of the same power, since directional antennas focus their beam width on an area and omni antennas do not restrict their beam width. The problem with directional antennas is that to see in all directions, these antennas either have to rotate or multiple antennas need to be used.
Two exemplary submarine antenna systems that utilize a rotating directional antenna are the Submarine High Data Rate (SubHDR) and the Type 8B/J Mod 3. However, neither antenna fits inside a 4.75″ inner diameter (ID) submarine radome. SubHDR is a three-axis satellite communication (SATCOM) system that features a rotating directional antenna that fits in a very large enclosure (radome) that includes a half of a sphere of radius two feet sitting on top of a two foot diameter cylinder of height one foot that is on top of a one foot tall tapered cone. SubHDR, while utilizing a rotating antenna, is extremely large. Larger systems are easier to detect visually and by radar.
The Type 8B/J Mod 3 is similar to SubHDR in that it is a three-axis SATCOM system, but it fits inside a much smaller radome with an outside diameter of 7.5″. Antenna systems that have been used in 4.75″ ID submarine radomes have been non-rotating. These systems have either utilized omni-directional antennas (one antenna that transmits/receives in all directions) or an array containing more than one directional antenna. Using multiple antennas creates two disadvantages, spreading power among multiple antennas and requiring a larger enclosure to house the antennas. Using multiple antennas means that the power supplied to the system is split between each individual antenna, and therefore the range of the entire system is based on the power divided by the number of antennas used. Using multiple antennas also creates size constraints because the size taken up is always going to be larger that of one antenna. Therefore, a single directional antenna is desired that can be rotated as needed and can be contained within a smaller radome.